WO2007000788A1 - Ultralight airfoils for wind energy conversion - Google Patents

Abstract

A device (1) is described for generating energy, composed of at least two ultralight airfoils (3, 5) rotating along their own axis, which functionally reproduce the characteristics of a propeller. The ultralight airfoils (3, 5) which characterise such aerodynamic configuration use pulling means (9, 14, 20) to keep their shape when operating. An important weight reduction of the structure is thereby obtained, which allows different applications in the aeolian generation field.

Description

ULTRALIGHT AIRFOILS FOR WIND ENERGY CONVERSION

The present invention relates to ultralight airfoils, rotating along their own axis, for generating energy.

Kites, or semi-rigid wings, can be defined as aerodynamic structures which, to keep their shape during their use, need tie-rods (similar for example to those on a suspended bridge) . Kites or semi-rigid wings have been used so far essentially with sports objectives, thereby exploiting only a small part of the potentialities of these new aerodynamic structures.

In the first steps in the history of flight, it was frequent to see the use of aerodynamic structures reinforced by the use of tie-rods.

The improvement of material characteristics and the increases in speed in time have removed the use of such technology.

The use of tie-rods for reinforcing structures which are not rigid enough appears again with the Francis Rogallo wing in 1948 and with the following development of kites and ultra-light planes. However, strangely, the use of tie-rods, usually applied for enlightening and making it possible to build, for example, big sized bridges, has never been extended to the manufacturing of propellers, when from the propulsion type they were transformed into wind energy catching propellers .

The continuing use of traditional propellers in the aeolian sector in practice has prevented the development of aeolian generation techniques at a height, being the propellers weight an almost impossible constraint to win, as the prior arrangements demonstrate since they can operate only when there are very strong winds.

Object of the present invention is integrating the solutions applied in manufacturing kites or semi-rigid wings, also to the manufacture of more complex structures using as components many kites or the semi-rigid ultralight airfoils, making them rotate along their own axis, thereby realising an aerodynamic structure which emulates the performance of a propeller. The airfoils of the invention thereby provide a contribution for the development of a simple, economic and ecologic energy generating technology.

The above and other objects and advantages of the invention, as will appear from the following description, are obtained with ultralight rotating airfoils applied to a device for generating energy as claimed in claim 1. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

In the following description, the term "helikite" will designate the figure composed of two or more kite or semi-rigid wings, made rotate along their own axis, while the term "kite" will designate the airfoils which compose it, as can be seen in Figure 1.

The present invention will be better described by some preferred embodiments thereof, provided as a non- limiting example, with reference to the enclosed drawings, in which:

Figure 1 shows kites or semi-rigid wings made rotate along their own axis;

Figure 2 shows an aeolian tower with a helikite which replaces the traditional propeller;

Figure 3 shows the possibility of changing the kite profile through tie-rods till the complete kite bending;

Figure 4 shows the modification with a control cable of the kite profile in order to obtain differently oriented forces on the individual kite and a resulting force which allows the helikite to be placed with different angles with respect to the wind axis; Figure 5 shows a boat which uses an helikite as propulsor;

Figure 6 shows a system of helikites which generate energy by traction;

Figure 7 shows the system with no wind;

Figure 8 shows helikites with generator placed in the rotatin centre, pointing out the necessary weight to obtain a resisting torque; and

Figure 9 shows a system of counter-rotating helikites constrained to a rigid support.

There are several applications of this type of technology: the most immediate and important ones are those aimed to aeolian generation.

With the helikite (or device 1) it is possible, for example, to emulate the function of windmill propellers and, given the lightness of these systems, it is also possible to generate electric energy at great heights, exploiting the winds present thereat.

The invention is related to a device (helikite) 1 for generating energy, whose major characteristic is that it is composed of at least two ultralight airfoils 3, 5 mutually connected, at one end thereof and adapted to rotate around their own axis through a force applied by wind.

In particular, a first one 3 of such airfoils 3, 5 is connected at one end 7 thereof to first pulling means 9 and at another end 11 thereof to second pulling means 14, a second one 5 of such airfoils 3, 5 is connected at one end 16 thereof to second pulling means 14 and at another end 18 thereof to third pulling means 20, in which such first, second and thirs pulling means 9, 14, 20 are connected to pulling means 22 of the airfoils 3, 5.

In particular, the first, second and third pulling means 9, 14, 20 are composed of cables or tie-rods.

The enclosed Figures show some possible applications of the helikite 1.

Figure 2 shows, for example, a helikite 1 rotating on a fixed support. The application of an helikite 1 to an aeolian tower can replace a traditional propeller and rotate an alternator generating electric energy.

The helikite 1 will have to be equipped with rigid ribs, which allow transmitting the rotation torque to an alternator.

The check of aerodynamic airfoils 3, 5 of the helikite 1, in case of wind increase, can be given both by the elastic deformability of the airfoils 3, 5 themselves, and by the shape check, obtained by constraint cables 9, 14, 20 of the device 1 which allow, in addition to controlling its pitch, also its complete closure (Figure

3) . The thereby composed device 1 appears much lighter and inexpensive with respect to the manufacture of aeolian generators equipped with rigid blades. In big windmills, the weight of the invidual blades is tens of tons and the pitch check in addition to the airfoil modification, in case of wind blows, is slow and cumbersome.

Figure 4 instead shows the application of a helikite which, during its rotation, differently modifies the profile of the individual kites 3, 5.

By modifying the profile of the kites 3, 5 during their rotation, according to the same principles applied to helicopter blades, namely checking the shape of the individual kites 3, 5 according to their angular position when rotating, it is possible to obtain a resultant of the carrier forces which is not aligned with the wind axis. By using the force of gravity as angular reference, helikites 1 can be obtained which develop ascending forces, thereby oposite forces to the gravity one, or also through a control cable 22, 23, real driving forms within a predefined angle with wind. A possible positioning angle is thereby determined, exactly like in case of the "possible" navigation area which distinguishes the sailing boats .

In case of use of semi-rigid kites 3, 5, it will be enough to constrain the helikite 1 in a different point from the barycenter in order to obtain a carrier resultant not aligned with the wind axis.

Having available a thereby devised aerodynamic structure, a traction system and several systems for high aeolian generation become able to be realised.

Figure 5 shows the application of a helikite 1 for the traction of a boat 50.

Recently, some applications of traditional kites have been shown which operate as traction also for high tonnage ships 50: the application of a helikite 1 to this function optimises the system aerodynamic efficiency, increasing with the same intercepted wind surface the traction exerted on a moving body.

It is further possible, by modifying the aerodynamic profile of the kites 3, 5 when rotating, to obtain the positioning of the helikite 1 not axial with the wind direction, but in a more favourable direction with respect to the route to be followed.

The use of a small aerostatic balloon 30 allows keeping the helikite 1 at a height also in case of sudden wind drops, thereby avoiding encumbrances at ground level.

As regards energy generation through traction, the helikite 1, through a suitable orientation of the individual kites 3, 5 when rotating, produces an ascending W

force and a traction force on the constraining cables 22, 23.

The traction exerted on the constraining cables 22, 23 actuates, through a slow unwinding, a current generator 32 placed on the ground, as shown in Figure 6.

The ascending movement of the helikite 1 will be alternated to recovery steps during which, by radically modifying the aerodynamic figure, it will be possible to recover the helikite 1 with a very small energy waste.

Having taken back the system at the desired height with a simple manoeuvre of one of the two constraining cables 22, 23, it will be possible to make the helikite 1 assume the open configuration and start thereby a new traction cycle.

The ascending force of the balloon can be computed for compensating the weight of helikite and constraining cables 22, 23, in order to define the parking height, as can be seen in Figure 7.

As regards instead the energy generation by rotation, always by using the described configuration which creates an ascending force or also using the aerostatic balloon 30 which keeps the system at a height, it will be possible to choose an energy generation by exploiting the rotation that the helikite 1, equipped with rigid ribs, can impress to a generator 36 placed at a height. Such arrangement had already been devised with other designs which however provide for the use of rigid blades: the weight of a system which uses rigid blades creates enrmous limits, and perhaps an impossible realisation.

The new-generation generators 36 are characterised by a core of permanent magnets and allow high weight reductions, in addition to the production of energy at very high voltages and that can be easily transferred also with cables with a small section.

The alternator can be placed at the helikite 1 centre, while, in order to counteract the rotation torque linked to energy production, a resisting torque will be necessary that can be easily obtained with weights 38 which are rigidly spaced from the rotation centre of the generator 36, as can be seen in Figure 8.

For system with higher power, to avoid problems deriving from the rotation torque, it is possible to imagine many helikites, counter-rotating on the same axis with interposed generator or suitably spaced and secured to a rigid structure 40, which also supports the alternators, as can be seen in Figure 9.

Also in this case, in order to take back the structure to ground, it will be possible to proceed by modifying the aerodynamic figure of the kites 3, 5 with a second constraining cable 23 in order to facilitate the system recovery.

The use of an auxiliary aerostatic balloon 30 can allow keeping the system at a height even when there is no wind.

The problems due to the presence of helikites at a heigh which can be a danger for other airplanes can be easily solved with the creation of aeolian parks, signalled on GPS navigation maps, where the flight over them is forbidden.

The chance of operating with the helikite from any type of floating support allows positioning it also in deep sea waters, removing every environmental impact issue .

Claims

1. Device (1) for generating energy, characterised in that it is composed of at least two ultralight rotating airfoils (3, 5) , said airfoils (3, 5) being equipped with pulling means (9, 14, 20) for keeping their aerodynamic shape during their use, said airfoils (3, 5) being mutually connected and rotated around their own axis through a force applied by wind, thereby emulating a propeller performance.

2. Device (1) according to claim 1, characterised in that a first one (3) of said airfoils (3, 5) is connected at one end (7) thereof to first pulling means (9) and at another end (11) thereof to second pulling means (14), a second one (5) of said airfoils (3, 5) is connected at one end (16) thereof to said second pulling means (14) and at another end (18) thereof to third pulling means (20) , said first, second and third pulling means (9, 14, 20) being connected to pulling means (22) of said airfoils (3, 5) for controlling their aerodynamic figure shape.

3. Device (1) according to claim 1 or 2, characterised in that it is operatively connected to a fixed support (24) for replacing a traditional propeller and rotating an alternator generating electric energy, said device (1) being equipped with rigid ribs adapted to allow transmitting a rotation torque to an alternator and being adapted, through a shape controlling cable (23) , to completely change its own profile .

4. Device (1) according to claim 1 or 2, characterised in that it is adapted, during rotation, to modify each one of its individual airfoils (3, 5) independently, according to the same principles applied to helicopter blades, namely controlling the shape of individual airfoils (3, 5) depending on their angular position when rotating, obtaining a resultant of lift forces not aligned with a wind axis, said device (1) being adapted to be used both as traction system, and as aeolian generating system at a height.

5. Device (1) according to claim 4, characterised in that it is adapted to operate by traction axial with wind or modifying the aerodynamic profile of the airfoils (3, 5) when rotating, to position the device (1) not axial with the wind direction, but along a direction complying with the route to be followed.

6. Device (1) according to claim 4, characterised in that it is adapted, by modifying the individual airfoils (3, 5) when rotating, to produce an ascending force and a traction force on constraining cables (22, 23) adapted to actuate, through a slow unwinding, a current generator (32) placed on the ground.

7. Device (1) according to claim 4, characterised in that it is adapted to generate energy by rotation and to be equipped with rigid ribs adapted to transmit its movement to a generator (36) placed at the device (1) centre, said device (1) being further equipped with weights (38) adapted to counteract a rotation torque linked to energy production, said weights (38) being rigidly spaced from a rotation centre of the generator (36) to create a resisting torque that countereacts the rotation torque.

8. Device (1) according to claim 7, characterised in that it is operatively connected to a plurality of other devices (1) counter-rotating on a same axis with an interposed generator (38).

9. Device (1) according to claim 7, characterised in that it is operatively connected to a plurality of other devices (1) spaced and secured to a rigid structure (40) which also supports the generators (38).

10. Device (1) according to any one of the previous claims, characterised in that it is equipped with a small aerostatic balloon (30) adapted to keep the device (1) at a height also in case the wind suddenly drops .